Question on trimming out Hobby Lobby Skimmer 400 - RC Groups
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Sep 24, 2002, 11:45 AM
Registered User
The Other Dave's Avatar

Question on trimming out Hobby Lobby Skimmer 400


I have 8 flights on my Skimmer 400 and I have some trim
questions.

Pics of plane in this thread

https://www.rcgroups.com/forums/show...threadid=62453

My setup is
Zagi speed 400 w/ 6x3 prop
8x1100 Hecell NIMH
2x hs81 metal gears
hitec 555
1/4 inch washout
AUW 20.5 oz

CG dead on 2.25 inches from leading edge.
I have the recomended amount of downthrust.

Overall I am very happy with it's flight characteristics. I have had
multiple 20+ minute flights w/ 5 flights to altitude (4 minutes of run time total). All of my flights have been in early morning (before 9 AM) so low/no thermals.

Here is the questions.

Under power with what I would call neutral trim (tail feathers
inline with elevator) it wants to pitch up to stall. With some downtrim this problem goes away. But should it be neutral.

During glide I also need some downtrim to avoid porpoising (sp?).
It will slowly pitch up approach stall, nose comes down and it will
accelerate.

Is this a CG problem or possibly an angle of incidence issue.
As I said everything is to the plan.

Thanks,

Dave
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Sep 24, 2002, 12:31 PM
Crashez-vous sans stress!
Dan H.'s Avatar
Try shimming up the trailing edge of the wing in 1/8th inch increments. You may also benefit from moving the CG back, also in small increments (don't try both modifications at the same time until you have an idea of what they do for you separately). Good luck and have fun!
Sep 24, 2002, 02:06 PM
Registered User
My skimmer does the same thing. Our club "expert" advised me to learn to change the elevator trim when transitioning from power to glide. Example: from a flat glide, going to full throttle requires 20% more down trim. It has become automtic for me to do this now. I think that this continous monitoring of the trim conditions has also improved my flying technique with the more advanced sailplanes (six servos) I've progressed to in the last 2 years.

Warren